Bump flask-restful from 0.3.8 to 0.3.9

Bumps [flask-restful](https://github.com/flask-restful/flask-restful) from 0.3.8 to 0.3.9.
- [Release notes](https://github.com/flask-restful/flask-restful/releases)
- [Changelog](https://github.com/flask-restful/flask-restful/blob/master/CHANGES.md)
- [Commits](flask-restful/flask-restful@0.3.8...v0.3.9)

---
updated-dependencies:
- dependency-name: flask-restful
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -18,7 +18,7 @@ Flask-HTTPAuth==4.1.0
 Flask-Migrate==2.5.3
 Flask-Mail==0.9.1
 Flask-OAuthlib==0.9.4
-Flask-RESTful==0.3.8
+Flask-RESTful==0.3.9
 Flask-Script==2.0.6
 Flask-SQLAlchemy==2.4.4
 flask-swagger==0.2.14